Vitamin D is a fat-soluble vitamin that occurs naturally in a few types of food and can be obtained as a dietary supplement. The vitamin can also be produced when the ultraviolet rays from the sunlight stroke the skin, triggering vitamin D synthesis.
The vitamin has many health benefits, including maintaining healthy and strong bones by helping the body absorb calcium, one of the body’s main building blocks. Vitamin D is also essential to the body as it performs a multitude of roles, including promoting healthy communication between the brain and the nerves and boosting the immune system to fight off invading bacteria and viruses.
Calcitriol, the active form of vitamin D, is made from the kidneys. It is considered a steroid hormone that has long been known for its role in regulating the levels of calcium and phosphorus and in mineralization of bones. Calcitriol is also a biologically active calcotrophic hormone with anticarcinogenic, antipsoriatic, anti-osteoporotic, immunomodulatory, and mood-modulatory properties.
The National Health Service (NHS) recommends taking 10 micrograms of vitamin D every day to keep the bones and muscles healthy.
How can vitamin D fight COVID-19?
Vitamin D has made the rounds as has been dubbed as a potential protective vitamin against the novel coronavirus. However, the role of vitamin D in the prevention and treatment of respiratory infections dates back in the 1930s, when cod liver oil was examined as a means to reduce industrial absenteeism due to common colds.
In a new report published in The Lancet, a team of researchers discussed the possibility that vitamin D could offer protection against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. The meta-analyses of randomized controlled trials performed from 2007 to 2020. The studies revealed that vitamin D has protective effects against acute respiratory infections.
The researchers observed that the risk factors for severe COVID-19 are akin to those of vitamin D deficiency. These include obesity, older age, and Black or Asian ethnic origin. They hypothesized that supplementation with vitamin D could become protective, preventive, or therapeutic against COVID-19.
Host immune responses
In the article, the authors said there are reasons why vitamin D induce host responses to SARS-CoV-2, early on in the infection, and in the latter stages of the illness. Previous studies have shown that vitamin D supports the body’s natural antiviral effector mechanisms, such as antimicrobial peptides and autophagy.
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Antimicrobial peptides (AMPs), also known as host defense peptides, are short positively charged peptides that can kill microbial pathogens directly. Autophagy, also known as “self-eating,” is the body’s process of cleaning out damaged cells to regenerate healthier ones.
The authors wrote that laboratory data showing the effects of Vitamin D on host response to the novel coronavirus are scarce. However, one study had shown that when the scientists screened four compound libraries for antiviral activity, they found that vitamin D’s active metabolite, 1,25-dihydroxyvitamin D, has an inhibitory effect in human epithelial cells that are infected with SARS-CoV-2.
Also, the vitamin has shown to help regulate immunopathological inflammatory responses in respiratory infections.
Vitamin D and severity of COVID-19
Previous research investigated the link between circulating levels of 25-hydroxyvitamin D (25(OH)D), which is a biomarker of vitamin D status of the body, and the incidence and severity of SARS-CoV-2 infection.
Two studies have shown inverse relationships between national estimates of vitamin D levels or status and the incidence of COVID-19, including the mortality in European countries.
The study has shown that when there are lower concentrations of 25(OH)D, the risk or susceptibility to COVID-19 increases. Also, the study revealed that COVID-19 severity increases when there are low levels of Vitamin D in the body.
Also, airway diseases are tied to dysregulated vitamin D metabolism, increasing the possibility that vitamin D deficiency may become a complication of inflammation in the respiratory tract.
Other studies highlight the potential for reverse causality, which means that low levels of vitamin D may lead to a higher incidence and severity of COVID-19.
The researchers noted that further studies are needed, involving well-powered randomized controlled trials of vitamin D supplementation in preventing and treating COVID-19 patients.
Vitamin D as prophylaxis
In a study published in on the preprint server bioRxiv*, a team of researchers claimed that calcitriol exhibits significant potent activity against SARS-CoV-2, paving the way for the development of host-directed therapies for ring prophylaxis of contacts of COVID-19 patients.
Further, the report enlightened on the use of vitamin D on COVID-19 patients. Many hospital-based treatment trials have been registered, which focused on vitamin D supplementation in severe COVID-19.
For instance, another study published on the medRxiv* preprint server suggested that vitamin D supplementation has been proven to be safe and has helped reduce the risk of acute respiratory infection (ARI), which is the initial infection seen in most COVID-19 patients.
Still, more research is needed to see the benefits of vitamin D supplementation in reducing the risk of severe COVID-19. The authors recommend taking vitamin D supplements since there is nothing to lose when taking them, and might even be more beneficial since vitamin D has many other health benefits.
bioRxiv and medRxiv publish preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.
National Institutes of Health (NIH). (2020). https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/
Martineau, A., and Forouhi, N. (2020). Vitamin D for COVID-19: a case to answer? The Lancet. https://www.thelancet.com/journals/landia/article/PIIS2213-8587(20)30268-0/fulltext
Mok, C.K., Ng, Y.L., Ahidjo, A. et al. (2020). Calcitriol, the active form of vitamin D, is a promising candidate for COVID-19 prophylaxis. BioRxiv. https://www.biorxiv.org/content/10.1101/2020.06.21.162396v1
Jolliffe, D., Camargo, C., Sluyter, J. et al. Vitamin D supplementation to prevent acute respiratory infections: systematic review and meta-analysis of aggregate data from randomised controlled trials. MedRxiv. https://www.medrxiv.org/content/10.1101/2020.07.14.20152728v1